This invention relates to electric contacts including single or multi contacts for connectors for use in relays, switches and the like, and more particularly to electric connectors comprising such single contacts or multi contacts.
Contacts for use in connectors, relays, switches and the like are required to have high conductivity and springiness in their nature. In general, however, metals having the higher conductivity exhibit the lower springiness, while metals having the higher springiness exhibit the lower conductivity. There has been no metal fulfilling the two requirements, that is, the high conductivity and springiness, simultaneously.
Therefore, copper alloys such as phosphor bronze are generally used, which fulfil the above requirements to a certain extent. However, even such a copper alloy, which is generally recognized to be most suitable for this purpose, has a much lower conductivity than that of pure copper and silver. In order to obtain contacts of high conductivity having the required springiness, therefore, high resilient metals should be used or sectional areas of the contacts should be made large to improve their conductivity, so that the contacts unavoidably become large. Accordingly, the miniaturization of contacts would encounter a limitation due to these factors. This limitation makes it difficult to realize connectors of small size and high performance which have been required to realize small-sized and high-performance electronic equipment.
Moreover, copper alloys to be used as spring materials are generally not only very expensive but also very troublesome in production processes, inasmuch as they need high accuracy heat treatment by precisely controlling temperature, time and atmosphere. Contacts made of such alloys are naturally expensive.
In order to eliminate the above disadvantages, it has been attempted to joint or laminate a high springiness metal and a high conductivity metal by pressure welding, electrolytic process or vapor deposition to obtain contacts having high conductivity and springiness. However, with these methods directly jointing the different metals, diffusion between them progresses step by step with the lapse of time to change compositions and conditions of the metals, so that the initial characteristics of the metals change so as to lower the performance of the contact. Moreover, the different kinds of metals tend to cause local batteries which would cause corrosion of the metals to lower their performance. Accordingly, it has been difficult to produce small-sized and high-performance contacts.
In prior art multi contacts connectors, moreover, single contacts 1 made of a copper alloy as above described are inserted into fixing apertures 2a of an insulating housing 2 and fixed thereat as shown in FIGS. 1a and 1b. In order to make smaller the connectors, when the number of the contacts per a constant distance is increased, intervals between the fixing apertures 2a become unavoidably smaller. Accordingly, it is limited in cost and material to make small the insulating housing. In fixing the single contacts inserted in the fixing apertures of an insulating housing, moreover, the more the number of the single contacts and the smaller the contacts, the more difficult is the assembling of the connector.
In order to avoid this difficulty, a method has been proposed in that a series of required plural contacts 1 whose ends are connected by a connecting piece 3 are made and are simultaneously inserted into fixing apertures of an insulating housing and thereafter the contacts are separated by cutting the connecting piece 3 along a line A as shown in FIG. 2. However, as a certain extent achievement of the miniaturization and high density application of the contacts to an insulating housing, the mechanical strength of the contacts is unavoidably lowered and intervals between the fixing apertures are minimized. As the result, in a step of transferring a series of contacts produced in a press to an assembling station, the intervals and positions of the contacts become irregular owing to their entanglement and deformation, so that the insertion of the contacts into the apertures becomes difficult making it impossible to assemble the connector with high productivity. Moreover, it is troublesome to cut off the connecting pieces 3 after insertion of the contacts.
As shown in a perspective view of FIG. 3a, it has been proposed to make multi contacts comprising a plastic layer 4, metal layers 5 of high conductivity and metal layers 6 of high springiness to form contacts 7 which are in the form of stripes arranged in rows with required intervals and have contact elements 7a and terminal elements 7b, respectively. In such multi contacts, the metal layers 6 of high springiness may be formed by a common single metal plate as shown in FIG. 3b. It is furthermore proposed to make multi contacts comprising a plastic layer 4 having a springiness and stripe contacts 7 formed on one surface of the plastic layer 4 in rows with required intervals as shown in FIG. 3c.
With these multi contacts, respective contacts 7 form a unitary body with the aid of the plastic layer 4. A common plastic layer 4 formed with two groups of multi contacts 8 and 9 as shown in FIG. 4a is folded such that metal layers 5 of high conductivity are on outer sides as shown in FIG. 4b, and thereafter the folded assembly is held by insulating blocks 10 and 21 as shown in a sectional view of FIG. 4c to form a male connector. A reference numeral 12 in FIG. 4c denotes extending contact elemets. Such a multi contact connector is therefore easily manufactured in comparison with a multi contact connector whose single contacts are inserted into apertures formed in an insulating block and fixed thereat. Moreover, by utilizing the etching method, a plurality of small contacts can be exactly formed with narrow intervals. Furthermore, these multi contacts comprise the separate metal layers exhibiting the high conductivity and springiness, so that they do not have the disadvantage in that sectional areas of the contact should be made large to improve their conductivity as contacts made of copper alloys which simultaneously fulfil the requirements of conductivity and springiness. Accordingly, small-sized multi contact connectors can be realized which have high connecting performance and other superior characteristics.
With such multi contacts, however, the metal layers are provided on a common flat plastic layer to form the contacts 7, so that their terminal elements are unavoidably flat. Such flat terminal elements do not determine positions of lead wires for other circuits. As the result, when the contacts 7 are arranged with narrow intervals, there is a risk of a lead wire 13 being soldered to a terminal element 7b at 14 to closely adjacent to a next lead wire as shown in FIG. 5a and there is a further risk of solder 14 extending over two terminal elements 7b to short-circuit therebetween. In order to avoid these risks, distances between the contacts must be enlarged, so that small-sized connectors cannot be accomplished.
With such multi contacts, moreover, the metal layers 5 for the springiness are generally made of a stainless steel alloy which is inferior in not only conductivity but also soldering capability. In a connector having contacts whose terminal elements 24b are inserted in apertures 26a formed in a printed circuit board 26 and connected to conductive elements 26b by means of molten solder bath method, therefore, the molten solder 27 tends to concentrate on a side of the metal layers 22 of conductivity, so that the solder 27 does not extend uniformly about terminal elements 24b of the contacts. As the result, the amount of the solder to be attached would become insufficient and cause defective soldering. Moreover, when a mating connector is removed from the connector fixed to the printed circuit board, the soldered portions of the terminal elements 24b are prone to failure owing to forces acting upon the soldered portions, whereby the connections tend to become incomplete. Accordingly, a connector superior in connection cannot be realized.
In order to solve this problem, it is considered that the terminal elements 24b are coated with metal layers by plating, such as tin, copper, silver or gold or alloys including these metals which are superior in soldering capability or pins 22' having circular or square cross-sections are fixed to the metal layers 22 of conductivity of the terminal elements 24b as shown in FIG. 7. However, when these are carried out, separate steps are necessary to make complicated the manufacturing processes.